Go Threads experiment - write system calls block

gothreads-experiment.go

package main

import (
	"fmt"
	"os"
	"sync"
)

var (
	dir       = "/tmp/writetest"
	buf       = []byte{}
)

func writeTask(id int) error {
	f, err := os.Create(fmt.Sprintf("%s/%d", dir, id))
	if err != nil {
		return err
	}

	for times := 0; times < 10000; times++ {
		_, err = f.WriteAt(buf, 0)
		if err != nil {
			return err
		}
	}

	return f.Close()
}

func parallelWrite(n int) {
	wg := sync.WaitGroup{}
	wg.Add(n)

	for i := 0; i < n; i++ {
		go func(k int) {
			err := writeTask(k)
			if err != nil {
				fmt.Printf("Thread %d: %v\n", k, err)
			}
			wg.Done()
		}(i)
	}
	wg.Wait()
}

func main() {
	buf = make([]byte, 1000000)
	parallelWrite(1000)
}

If you run the above program, and run ps huH p <PID_OF_PROCESS> | wc -l in a shell, you get the OS thread count of the process. The number of threads is always close to the argument of the parallelWrite() call.